2012 VP113

• 1. Introduction

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  2012 VP113 sits at the farthest known perihelion of any object in our Solar System. Its closest approach to the Sun never brings it within 80.5 astronomical units of our star. To put that in perspective, Pluto sits around 39 astronomical units from the Sun at its nearest. Scott Sheppard and Chad Trujillo, two American astronomers working at Cerro Tololo Inter-American Observatory in Chile, discovered it on the 5th of November 2012. They gave it a nickname almost immediately: Biden, after then-Vice President Joe Biden, because the letters "VP" appeared in its official designation. The discovery was not announced to the public until the 26th of March 2014, more than a year after it was first spotted. What is this distant, reddish world? Where exactly does it belong in the Solar System's family? And what does its orbit tell us about forces we have not yet seen?

• 2. The Discovery Story

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  The first observation came through NOAO's 4-meter Víctor M. Blanco Telescope at Cerro Tololo Inter-American Observatory. That initial detection, logged on the 5th of November 2012, put the object on the radar of a very small circle of scientists. For the months between discovery and public announcement, only two observatories tracked it: Cerro Tololo Inter-American Observatory, designated station 807, and Las Campanas Observatory, designated station 304. Carnegie's 6.5-meter Magellan telescope at Las Campanas Observatory in Chile was used to nail down its orbit and study its surface properties. Researchers also found the object hiding in precovery images dating as far back as September 2007, meaning it had been captured on camera years before anyone realized what they were looking at.

• 3. A World Without a Ruler

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  2012 VP113 has an absolute magnitude of 4.05, a measure of intrinsic brightness that suggests it may be large enough to qualify as a dwarf planet. No one has measured its diameter or albedo directly. Assuming a moderate geometric albedo of 0.15, which is typical for trans-Neptunian objects, the diameter works out to around 450 kilometers. Astronomers expect it to be about half the size of Sedna, and roughly similar in size to Huya. Its surface has a moderately red color, produced by radiation acting on frozen water, methane, and carbon dioxide. That reddish tint is actually a chemical clue: it points toward formation in the gas-giant region of the Solar System rather than in the classical Kuiper belt, which tends to produce ultra-red colored objects. The Hubble Space Telescope is planned to image 2012 VP113 in 2026, an observation that should reveal whether it has any significantly sized moons.

• 4. Orbit at the Edge

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  2012 VP113 holds a record that no other known Solar System body can claim: the farthest perihelion of any known minor planet or any other known object. Its closest approach to the Sun exceeds even Sedna's perihelion, though its aphelion is only about half of Sedna's. It qualifies as a sednoid, the second one ever discovered, defined by a semi-major axis beyond 150 astronomical units and a perihelion greater than 50. The giant planets sit too far inside to have any meaningful gravitational grip on it. Its last perihelion occurred within a couple of months of September 1979. Sheppard and Trujillo noticed that 2012 VP113 shares orbital traits with other extreme trans-Neptunian objects. In fact, all known Solar System bodies with semi-major axes over 150 and perihelia beyond Neptune cluster their arguments of perihelion near 340 degrees. That clustering led the two astronomers to propose that an undiscovered body, now referred to as Planet Nine, is steering these distant objects into similar orbits.

• 5. Origins and Hypotheses

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  How 2012 VP113 wound up with a perihelion so far beyond the Kuiper belt is genuinely unknown. Several explanations have been proposed. A passing star could have pulled its orbit outward. A trans-Neptunian planet several times the mass of Earth, sitting hundreds of astronomical units from the Sun, could be responsible. The region beyond Pluto may even contain more than one such unseen planet. Scientists also consider the possibility that 2012 VP113 was captured from a completely different planetary system. The leading hypothesis, though, is that multiple gravitational interactions within the crowded open star cluster where the Sun formed gradually raised its perihelion to its current extreme distance. 2012 VP113 may also belong to a hypothesized region called the Hills cloud. The scarcity of objects with perihelia near 50 astronomical units is itself significant: it does not appear to be an accident of observation, and is referred to as the Kuiper cliff. That gap in the population is a puzzle astronomers are still working to explain.